Systematic experiments have been conducted to study the effects of various operating parameters on the performances of a direct methanol fuel cell (DMFC). The effects of cell operating temperature, methanol concentration, anode flow rate, air flow rate, and cathode humidification have been studied. The experimental results showed that all the studied operating parameters, except the cathode humidification, have significant effects on the DMFC cell performances, and the cathode humidification has almost negligible effect. The study revealed that the detrimental effect of methanol crossover can be alleviated by increasing cathode air flow rate or oxygen partial pressure. This result showed that the cathode structure and operating condition may play a very important role in DMFC design and operations. The experimental results are presented in both graphical and tabular forms. (c) 2004 Elsevier B.V. All rights reserved.